n-Type thiophene semiconductors

ABSTRACT

The new fluorocarbon-functionalized and/or heterocycle-modified polythiophenes, in particular, α,ω-diperfluorohexylsexithiophene DFH-6T can be straightforwardly prepared in high yield and purity. Introduction of such modifications to a thiophene core affords enhanced thermal stability and volatility, and increased electron affinity versus the unmodified compositions of the prior art. Evaporated films behave as n-type semiconductors, and can be used to fabricate thin film transistors with FET mobilities ˜0.01 cm 2 /Vs—some of the highest reported to date for n-type organic semiconductors.

This application claims the benefit of prior provisional patentapplication No. 60/220,601, filed Jul. 24, 2000, the entirety of whichis incorporated herein by reference.

The United States Government has rights in this invention pursuant toGrant No. N00421-98-1187 from DARPA and the NSF-MRSEC program(DMR-9632472) to Northwestern University.

BACKGROUND OF THE INVENTION

Thiophene chemistry and the chemical stability of the thiophene ringhold potential for use of thiophene materials in molecular-basedelectronics and photonics. In particular, αα′-conjugated thiopheneoligomers (nTs) and polymers (polythiophenes-PTs) have attracted greatinterest as semiconducting elements in organic thin-film transistors(TFTs).^([1,2]) To be useful in such devices and related structures, the

organic material must support a channel of holes or electrons (p- orn-type semiconductor, respectively) created by the gate electrode bias,which switches the device “on”. Furthermore, the charge mobility of thematerial must be sufficiently large to increase the source-drainon-conduction by many orders of magnitude over the “off” state. Thedensity of the charge carrier in the channel is modulated by voltageapplied at the gate electrode.

To date, the most noteworthy examples of this family of compounds areunsubstituted, α,ω- and β,β′-dialkylsubstituted nT (n=4,6), andβ-alkylsubstituted PT, where optimized carrier mobilities (0.1-0.6 cm²V⁻¹ s⁻¹) and on/off ratios (>10⁶) approach those of amorphoussilicon.^([1e,2a,c,e,3]) However, without exception, these systemsfacilitate hole injection and behave as p-type semiconductors,presumably because the thiophene electron-richness renders negativecarriers susceptible to trapping by residual impurities such asoxygen^([4]). Even so, increasing the number of thiophene unitsdecreases dramatically environmental (air, light) stability and causesprocessing and purification difficulties.

Electron transporting (n-type) organic materials are relatively rare.However, developing/understanding new n-type materials would enableapplications^([5]) such as bipolar transistors, p-n junction diodes, andcomplementary circuits as well as afford better fundamentalunderstanding of charge transport in molecular solids. The major barrierto progress however, is that most n-type organics are eitherenvironmentally sensitive, have relatively low field mobilities, lackvolatility for efficient film growth, and/or are difficult tosynthesize.^([5e,6,7])

As indicated by the foregoing notations, these and other aspects of andteachings of the prior art can be found in the following:

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SUMMARY OF THE INVENTION

As shown from the above discussion, there are a considerable number ofproblems and deficiencies associated with the prior art relating touseful organic n-type semiconductor compounds, compositions and/ormaterials, including those discussed above. There is a demonstrated needfor such materials, compositions, layers and/or composites for thin filmdeposition and related applications useful in conjunction with thefabrication of thin film transistors and related devices as can beincorporated into an integrated circuit.

Accordingly, it is an object of the present invention to provide new anduseful n-type organic materials, together with one or more methods ofpreparation, overcoming those various shortcomings and deficiencies ofthe prior art.

It will be understood by those skilled in the art that one or moreaspects of this invention can meet certain objectives, while one or moreother aspects can meet certain other objectives. Each objective may notapply equally, in all instances, to every aspect of the presentinvention. As such, the following objects can be viewed in thealternative with respect to any one aspect of the present invention.

It is another object of the present invention to provide a facile,efficient synthetic method for the preparation of an n-type thiopheneconductive material, such preparation resulting in high yield and purityof the desired thiophene material.

It is yet another object of the present invention to provide n-typesemiconducting thiophene compounds and related materials and/or thinfilms which can be used in the fabrication of and in conjunction with avariety of circuitry related devices, including, but not limited to,diode, bipolar junction transistor and field-effect transistor (eitherjunction or metal-oxide semiconductor) devices.

It is yet another object of the present invention to provide for thesynthetic modification of organic semiconductive molecular solids toalter electronic behavior, in particular the use of such modifiedthiophenes to provide and facilitate electron transport.

Other objects, features, benefits and advantages of the presentinvention will be apparent from the foregoing, in light of the summaryand the examples and descriptions which follow, and will be readilyapparent to those skilled in the art having knowledge of varioussemiconducting materials, their preparation and subsequent use. Suchobjects, features, benefits and advantages will be apparent from theabove as taken in conjunction with the accompanying examples, tables,graphs, data and all reasonable inferences to be drawn therefrom.

In accordance with one aspect of the present invention, one or more ofthe foregoing objects can be achieved by use of one or more of thethiophene compounds, compositions and/or materials of the type describedherein, and/or with a suitable substrate material as part of a compositeor a device incorporating such a composite.

In accordance with another aspect of the present invention, one or moreof the preceding objects can be achieved with a method described herein,including the use of a thiophene material as an n-type semiconductor totransport electrons.

In accordance with another aspect of the present invention, one or moreof the foregoing objects can be achieved with an organic thin filmtransistor device which includes a source electrode, a drain electrodeand a semiconductor material between the electrodes, the materialpreferably comprising an n-type fluoroalkyl-substituted polythiophenecomposition.

In accordance with yet a further aspect of the present invention, amethod is provided by way of using introduction of substituents to asemiconducting composition to alter charge conduction there through,such that a material which would otherwise be considered a p-typeconductor becomes an n-type conductor through a synthetic transformationof the type described herein. Various other properties such as band gap(expansion), electron mobility (increased), electron affinity(increased) and ionization potential (higher) are similarly altered.

The present invention includes the first n-type thiophene semiconductorcompositions and/or materials, for use with a variety of applications ordevices including, but not limited to, organic TFTs. A preferredthiophene composition/material comprisesα,ω-diperfluorohexylsexithiophene

designated as DFH-6T, shown above and as structurally compared to thesexithiophene (6T) and dihexylsexithiophene (DH-6T) compositions of theprior art. Fluoroalkyl functionalization of a thiophene coresignificantly alters the electronic, film growth, and semiconductingproperties of the resulting films.

The present invention contemplates, in part, a range of fluoroalkylatedcompositions and/or materials including the correspondingfluoroalkylated oligo- and polythiophene compositions. Fluoroalkylationincludes various alkyl chain lengths and fluoro-substitutions thereof,such as would result in an alteration to n-type semiconductivity, ascompared to p-type conductivity of the unaltered composition. Similareffects can be achieved by introduction/insertion of electron deficientmoieties, such as fluoro- and perfluoroaryl groups and variousheterocycles. Known synthetic procedures can be used or modified aswould be known to those skilled in the art made aware of this inventionto provide a variety of thiophene cores, each with the appropriateinsertions and/or fluoroalkyl substituents. However, for purposes suchas processing and subsequent device fabrication, a preferred core hasabout 4-7 conjugated thiophene units. Likewise, C₅-C₇ fluoroalkylsubstitution is preferred and can be accomplished usingcommercially-available reagents, but various other substitutions can beachieved through synthesis of the corresponding fluoroalkyl compounds.Thiophene core substitution and heterocycle insertion is, therefore,limited only by the desired degree of n-type semiconductivity.

A TFT device with, for instance, a DFH-6T active layer operates in then-type accumulation mode, indicating DFH-6T and other such thiophenecompounds are n-type conductors. Compared to prior art materials such asDH-6T and 6T, the new fluorinated thiophenes of this invention aresignificantly more chemically and thermally inert, and can betransported quantitatively into the vapor phase without decomposition.In the solid state, the inventive thiophene units have strong π-πintermolecular interactions. As described below, film growthmorphologies can depend on growth temperature and substrate pretreatmentand/or functionalization.

This invention demonstrates that fluoroalkyl functionalization of athiophene core substantially enhances thermal stability, volatility, andelectron affinity vs. the non-fluoro analogs and affords the firstn-type thiophene for use, as an example, in a TFT. As a representativematerial of this invention, DFH-6T film morphology is sensitive tosubstrate temperature and surface pretreatment, with crystallite sizeincreasing with increasing growth temperature. UV-vis/PL and XRD studiesindicate that while DFH-6T has close intermolecular π-stacking, it isnot isostructural with the DH-6T analog. Since thiophene oligomers ofthe prior art are typically p-type, the present invention using n-typesemiconductors can provide a pathway by which an all-thiophenecomplementary circuit can be realized.

In accordance with the preceding, the present invention further includesthiophene systems such as those represented by general structuralformulas 1-3, as can be prepared in high yield viapalladium(0)-catalyzed coupling of haloaromatics with stannyl (Stillecoupling) and Grignard reagents.

One embodiment of this invention includes various prefluoroalkyl and/orfluoroalkyl substituted thiophene oligomers or polymers, as can berepresented by the structural formula

wherein R₁, R₂ and R₃ are selected from the substituent group consistingof fluoroalkyl moieties, C_(n)H_(2n+1) and where n is about 1-12, H, Fand (CH₂)_(a)X and where a is about 1-12 and X is selected from thegroup consisting of amino, hydroxy and carboxylic acid functionalities;and x, y and z are integers from the group of integers consisting of 0and integers greater than 0.

The fluoroalkyl moieties of such compositions can include but are notlimited to the corresponding linear, branched and/or cyclicsubstituents, optionally in the presence of one or more alkyl and/orfluorine substituents. Alternatively, an alkyl substituent can furtherinclude a functional group including but not limited to those describedin Examples 14 and 15, below, such that the resulting polythiophenecomposition can be further transformed and/or modified. Various otherfunctional groups will be well known to those skilled in the art andmade aware of this invention, as will be the corresponding synthetictechniques/procedures by which to effect such a transformation orpolythiophene modification.

With respect to the aforementioned fluoroalkyl moieties, variousproperties of such compositions can be modified by alkyl length andextent of alkyl fluorination. Preferred compositions can include thosewith a fluoroalkyl moiety having the compositional formulaC_(n)F_(2n+1), where n is about 1-8. The compositions of suchembodiments can be further modified by choice of integers x, y and z.Regardless of substitution, such preferred embodiments can also includethose in which x is about 0-4, y is about 0-8 and z is about 0-12.However, it should be understood, in the broader context of thisinvention, that the composition of such polythiophenes and the number ofconjugated thiophene units is limited only by synthetic technique.

Representative structures include but are not limited to the following:

Compositions 1a-h were prepared according to Schemes 1 and 2. (See,also, Examples 17 and 17a-g.)

Another embodiment of this invention includes various π-conjugatedperfluorophenyl-thiophene oligomers, as can be represented by thestructural formula

wherein R₁, R₂ and R₃ are selected from the substituent group consistingof fluoroalkyl moieties, C_(n)H_(2n+1) and where n is about 1-12, H, F,and (CH₂)_(a)X and where a is about 1-12 and X is selected from thegroup consisting of amino, hydroxy and carboxylic acid functionalities;and x, y and z are integers selected from the group of integersconsisting of 0 and integers greater than 0.

The compositions of this embodiment and the chemical/physical propertiescorresponding thereto, can be modified as described above by choice andextent of thiophene substitution. In addition, as the present embodimentillustrates, the compositions of this invention can be further modifiedby insertion of perfluoroaryl components between conjugated thiopheneunits. Use thereof in combination with any of the aforementionedsubstitution parameters can provide a route to choice and design ofcompositions with specific electronic properties.

Representative structures include but are not limited to the following:

Compositions 2a-b were prepared according to Scheme 3. (See, also,Examples 18a-e.)

Another embodiment of the present invention includes variousπ-conjugated electron-poor heterocycle (including azine)-thiopheneoligomers, as can be represented by the following structural formula

wherein R₁, R₂ and R₃ are selected from the substituent group consistingof fluoroalkyl moieties, CH₂H_(2n+1) and where n is about 1-12, H, F,and (CH₂)_(a)X and where a is about 1-12 and X is selected from thegroup consisting of amino, hydroxy and carboxylic acid functionalities;x, y and z are integers selected from the group of integers consistingof 0 and integers greater than 0; and A, B, W and Z are selected fromthe group of moieties consisting of N and CH.

Modification of a polythiophene composition can also be achieved throughinsertion of a suitable heterocyclic component, the effect of which canbe comparable to perfluoro aryl substitutions of the sort describedabove. Several such insertions are illustrated, below, but thisembodiment can be extended to include other electron-deficientheterocycles including but not limited to thiadiazine and tetrazine.Polythiophene compositions including such components can be preparedthrough straight-forward extensions of the general synthetic techniquesdescribed herein, such extensions as would be understood by thoseskilled in the art. The electronic effect afforded such thiophenecompositions by heterocycle insertion can be further tailored for aspecific end-use application through choice and degree of substitution,as described more fully above. Accordingly, as with the precedingfluoroalkyl and perfluoroaryl compositions, the heterocycliccompositions of this embodiment can vary without limitationcorresponding to substituent (R₁, R₂ and R₃), optional functional group(amino-, hydroxy- or carboxylic acid groups), heteroatom identity and/ornumber of thiophene and/or heterocyclic units.

Accordingly, as also described elsewhere herein, the present inventioncan further include a method of using thiophene structural modificationto provide, promote and/or enhance n-type thiophene conductivity. Such amethod includes (1) preparing a polythiophene composition having aplurality of conjugated thiophene components or moieties; (2) providingthe composition a structural modification sufficient to promote n-typeconductivity, such a modification selected from the group of structuralmodifications described above and including but not limited tofluoroalkyl substitution, fluorine substitution, fluoroaryl insertion,heterocycle insertion and combinations thereof. As described herein andas would be understood to those skilled in the art, such modificationscan be made or provided en route to the preparation of suchpolythiophene compositions. Alternatively, various synthetic techniques,depending upon the desired modification, can be made subsequent thereto.Such modifications can provide a wide variety of polythiophenecompositions, commensurate with the broad scope of this invention, suchcompositions including but not limited to those embodiments discussedabove.Representative structures include but are not limited to the following:

Compounds 3a-d were prepared according to Scheme 4. (See, also, Examples19a-f).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows schematically a synthetic procedure, in accordance withthis invention, en route to a representative, but preferred n-typefluoroalkylthiophene material.

FIG. 2 shows DSC thermograms of DFH-6T (bold line) and DH-6T (fine line)under N₂. Temperature ramp=1.5° C./min.

FIG. 3 shows reduced pressure (0.01 torr N₂) TGA comparison of thevolatility characteristics of DHF-6T and DH-6T: weight loss comparisonplots (A) for DH-6T and DFH-6T recorded at a ramp rate of 1.5° C./min;and isothermal data (B) collected at 260 and 290° C. for DFH-6T andDH-6T, respectively.

FIG. 4 shows optical absorption (T-vis) and emission (PL) spectra ofDFH-6T (bold line) and DH-6T (fine line): (A) dilute toluene solution atca. 80° C., solution PL excited at 444 nm (DFH-6T) and 436 nm (DH-6T);and (B) as thin films (˜1.8 μm) on glass substrates, film PL spectraexcited at 377 nm (DFH-6T) and 363 nm (DH-6T).

FIG. 5 provides plan view SEM images of 100 nm thick DFH-6T filmsdeposited at various substrate temperatures on silicon: (A) 25° C., (B)85° C., and (C) 145° C.

FIG. 6 provides X-ray θ-2θ diffractograms of ˜2 μm thickvacuum-evaporated DFH-6T films grown on Si substrates at varioussubstrate temperatures. Note that the 240° C. spectrum corresponds to afilm grown at 200° C. and annealed at 240° C. for 30 min.

FIG. 7 plots graphically (A) source drain current vs. voltagecharacteristics of DFH-6T TFTs (top contact configuration) at differentgate voltages, and (B) source drain current vs. gate of DFH-6T TFTs.

FIG. 8 schematically illustrates several transistor and relatedintegrated circuit devices including therein, in accordance with thisinvention, a polythiophene thin film of the type described herein.

FIG. 9 provides a reduced pressure (0.01 torr) TGA weight losscomparison of the volatility characteristics of compositions 1e, 1h, 2a,2b, 3a, 3c, with reference to compositions 6T and DH-6T.

FIG. 10 shows UV-Vis absorption spectra of 1a-c, 1e, 1h in toluene.

FIG. 11 shows, comparatively, thin film (1.8 μm) UV-Vis/PL spectra of A)DH-6T, 1e, and 1h B) 2a, b.

FIG. 12 shows, comparatively, toluene solution (saturated) UV-Vis/PLspectra of A) DH-6T and 1h B) 2a, b.

FIG. 13 shows cyclic voltammograms illustrating the oxidation andreduction peaks of 2a-b.

FIG. 14 shows cyclic voltammograms illustrating the oxidation andreduction peaks of 1h and 3c.

FIG. 15 provides an X-ray diffractogram of approximately 2 μm-thickvacuum-evaporated film of 2a on silicon substrate grown at 25° C.substrate temperature.

FIGS. 16 and 17 provide molecular stacking diagrams illustratingmaterial structure and the resulting electrical properties in accordancewith those and various other compositions of this invention.

EXAMPLES OF THE INVENTION

The following non-limiting examples and data illustrate various aspectsand features relating to the thiophene compounds, composites, materialsand related methods and devices of this invention, and demonstrate theirsurprising and unexpected utility in the transport of electrons(n-type). Comparably utilities and advantages can be realized usingvarious other embodiments consistent with this invention.

Example 1

DFH-6T was synthesized in high yield via Pd⁰-catalyzed Stille couplingof 5-bromo-5′-perfluorohexyl-dithiophene (6) with5,5′-di(tributyl-stannyl)dithiophene (FIG. 1). This route affords DFH-6T(1) in high purity and yield (˜95%) after multiple gradient sublimation.Note that although monosubstituted perfluoroalkyl thiophene oligomers upto three units have been reported, synthetic yields were typically ˜10%.For example, 3′-perfluorohexylterthiophene was isolated in ˜11% yield.

Example 2

The comparative thermal properties of DFH-6T and DH-6T were investigatedby differential scanning calorimetry (DSC) and thermogravimetricanalysis (TGA). In the DSC, both compounds exhibit at least onetransition (FIG. 2). Compound DH-6T exhibits a distinctcrystal-to-liquid crystal (LC) transition at 292° C. and aLC-to-isotropic transition at 309° C., while the literature showscrystal-to-LC transition of 2 (300° C.) falls just below the meltingpoint, 308-313° C. These mesophase formation events are not surprisingin view of the molecular architectures. However, the most interestingfeature is that the two systems exhibit such similar thermal behaviorand almost identical melting points, suggesting that strong DH-6T π-πinteractions are preserved upon fluorine substitution.

Example 3

In contrast, the α,ω-fluorocarbon chains have a dramatic effect on thevolatility of DFH-6T as shown by TGA (FIG. 3A). The monotonic % weightloss vs. T demonstrates smooth, clean, quantitative sublimation wellbelow the melting point with negligible residue. In contrast, DH-6Texhibits significant volatility only above the melting point, with theTGA data revealing inflections at ˜298 and ˜306° C., suggestingdecomposition processes. In addition, a significantdecomposition-related residue (˜6%) is observed at 320° C. The enhancedvolatility of DFH-6T (vs. DH-6T) is further demonstrated by isothermalTGA (FIG. 3B) where DH-6T sublimation at the lowest possible temperatureleaves ˜8% decomposition residue.

Example 4

FIG. 4 shows optical absorption and emission (PL) spectra of DFH-6T andDH-6T in solution (FIG. 4A) and as thin vapor-deposited films (FIG. 4B).Remarkably, the solution spectra are nearly superimposable, arguing thatthe energy differences between ground and excited states of the 6T coreare only marginally sensitive to α,ω-substitution and that the HOMO-LUMOgaps of ˜2.4 eV are nearly identical. The spectra of the films exhibitboth differences and similarities. First, both PL spectra have a centralpeak and two weaker shoulders. The high energy shoulders fall, for bothsystems, at the same wavelength near the tail of the absorption,yielding estimated film HOMO-LUMO gaps of ˜2.2 eV. However, while DFH-6Texhibits strong green fluorescence (λ_(max)˜588 nm) under UV excitation,the DH-6T emission intensity is several orders of magnitude weaker andred-shifted by ˜30 mm. The low PL yields of the prior art DH-6T (2) and6T (3) thin films and blue-shifted absorption maxima vs. solution werepreviously ascribed to Davydov splitting. The origin of the DFH-6Tblue-shifted absorption and enhanced PL efficiency is unknown andwarrants further study. While both DH-6T and DFH-6T exhibit strongintermolecular π-π interactions, they are not isostructural (videinfra).

Example 5

The electronic consequences of DH-6T fluoroalkyl substitution were alsoinvestigated by cyclic voltammetry (one-compartment cell with a Ptworking electrode, Ag/0.1M AgNO₃ (CH₃CN) reference, Ag counterelectrodes). The Ag/AgNO₃ reference electrode was calibrated againstferrocene/ferrocinium (E_(1/2)=0.042 V). Voltammograms of DFH-6T andDH-6T in CHCl₃/0.10M TBABF₄ exhibit two chemically irreversibleoxidative waves at +0.68/+0.88 V and +0.41/+0.61 V, respectively, andnegligible reductive features, indicating chemically irreversibleoxidative processes likely related to polaron and bipolaron formation.The first and second anodic peaks of DFH-6T vs. DH-6T exhibit a uniformanodic potential shift (˜+0.27 V), indicating that introduction ofperfluoroalkyl chains on the 6T core substantially increases theionization potential.

Example 6

SEM reveals DFH-6T film growth depends significantly on substratetemperature and surface pretreatment. Films deposited at 25° C. consistof small crystalline grains (˜80×50 nm²) resulting from rapidcondensation on the cold substrate (FIG. 5A), while growth at 85° C.(FIG. 5B) affords elongated grains with larger dimensions (˜500×60 nm²)and random orientation. Growth at 145° C. yields larger crystallites(FIG. 5C: ˜1000×350 nm²), however film morphology is less smooth,probably because DFH-6T volatility prevents uniform adsorption on thehot surface. The influence of substrate temperature on crystallite sizeand film morphology for other thiophene semiconductors such as 6T isknown to be related to nucleation site density, growth rate, and surfacefree energy phenomena during growth. Because Si/SiO₂ has a hydrophilicnative oxide layer, the surface is not ideal for deposition of ahydrophobic adsorbate. Thus, substrates were also pretreated withCF₃(CF₂)₅CH₂CH₂SiCl₃ to produce a fluorocarbon monolayer. Thecrystallite dimensions are increased by ˜10% and grain-to-grain,grain-to-substrate interconnections are visibly enhanced. Various othersubstrate materials known to those skilled in the art can be used inconjunction with this invention, not only to further demonstrate theutility shown in this example, but also in the various composites andelectronic devices described elsewhere herein.

Example 7

X-ray diffraction (Cu K_(α)) scans of DFH-6T films grown at varioustemperatures (FIG. 6) reveal that higher crystalline order is achievedas the substrate temperature is increased to 200° C. Annealing at 240°C. further enhances microstructural alignment, with the dominant Braggfeatures assignable to a family of (n00) reflections corresponding to areal-space periodicity of 36.1±0.2 Å, close to the DFH-6T long axisdimension. Although the crystal structure of DFH-6T has not beendetermined, the XRD data suggest preferential molecular orientation withlong axes along the substrate normal, in which case transport in theplane of the film would benefit from close π-π stacking. Note thatDFH-6T films grown on CF₃(CF₂)₅CH₂CH₂SiCl₃-treated Si substrates exhibitsharper XRD reflections, indicating highly ordered films. Finally,powder diffraction reveals that DFH-6T and DH-6T are not isostructural,with different unit cell arrangements expected in view of the differentpacking properties of hydrocarbon vs. perfluorocarbon chains.

Example 8

Demonstrating use of the present invention in conjunction with a thinfilm as part of a field effect transistor (FET), field-effectmeasurements were carried out on top contact TFTs with 30-100 nm DFH-6Tfilms deposited at <10⁻⁶ mbar and at ˜0.5-1.0 Å/s onto n⁺-Si FETsubstrates with a 230 nm dry thermal SiO₂ insulating layer. Thesubstrate temperature was varied between 50° C.-120° C. Prior to DFH-6Tdeposition, the SiO₂ surface was silylated with hexamethyldisilazane orCF₃(CF₂)₅CH₂CH₂SiCl₃; both yielded similar TFT results. The devices werecompleted by evaporating Au or Al source-drain contacts on the DFH-6T.Device characteristics were measured under N₂ with an HP parameteranalyzer. FIG. 7(a) shows characteristics of a typical DFH-6T FET withAu S-D contacts (channel length L=75 μm, channel width W=1.5 mm).Transistor action is observed only for positive gate voltages (V_(g)>0)indicating an accumulation layer of mobile electrons is formed at theDFH-6T-SiO₂ gate dielectric interface. No transistor action is inducedby applying a negative gate voltage. Previously, only p-typeaccumulation (V_(g)<0) has been observed in TFTs of alkyl-substitutedand unsubstituted oligo- and polythiophene derivatives. The positivesigns of both gate voltage (V_(g)) and source drain current (I_(d)) showthat DFH-6T is a new n-type semiconductor. The present n-type conductiondoubtless reflects the greater electron affinity of the fluoroalkyl-substituted sexithiophene.

It is remarkable, surprising and unexpected that this relatively minorsubstituent-related change is sufficient to dramatically alter thin-filmsemiconducting properties from p- to n-type. The only other example ofsuch a majority carrier sign inversion is the unrelatedphthalocyanine→perifluorophthalocyanine system. However, DFH-6T andM(F₁₆Pc) differ markedly in the nature of substituent effects, and theinversion observed here would not be expected. In the M(F₁₆Pc) system,extensive C—H→C—F substitution leads to a large electronic perturbationsof the core structure. Furthermore, the nature of the substituentsdiffers. Whereas perfluoroalkyl chains exhibit only strong σ-inductiveelectron-withdrawing effects (−I), F atoms attached directly toπ-systems exhibit both donating-resonance (+R) and attracting-inductive(−I) characteristics.

Example 9

The device of FIG. 7 was fabricated with Au source-drain contacts.Devices with Al contacts exhibit similar characteristics, which issurprising considering the significantly higher Au work function (5.1eV) vs. Al (4.3 eV), implying, a priori, a higher barrier for electroninjection from Au. Values for the field-effect mobility were determinedfrom the transfer characteristics in the saturation regime (FIG. 7 b).The highest mobilities of 0.02 cm²/Vs$\frac{\mathbb{d}I_{d}}{\mathbb{d}V_{g}} = {\frac{C_{i} \cdot W}{L} \cdot {\mu_{FET}^{sat}\left( V_{g} \right)} \cdot \left( {V_{g} - V_{T}} \right)}$were obtained for film growth at 80-100° C. For growth temperatures˜50°, significantly lower mobilities (<10⁻⁴ cm²/Vs) are observed, andfor temperatures ˜120° C., a reduced mobility is obtained. This optimumsubstrate temperature doubtless reflects, among other factors, the grainsize distribution temperature dependence in the polycrystalline film.The on/off ratio in these DFH-6T devices is as high as 10⁵. The devicesexhibit relatively high turn-on voltages V_(o) of 25-35V, indicating acertain fraction of the induced electron carriers occupies localizedtrap states. The turn-on voltage increases further during operation.This results in a decrease of the TFT ON-current as a function of timewhich manifests itself in a non-ideal negative slope of the outputcharacteristics in the saturation regime (FIG. 7(a)). Theturn-on-voltage can be somewhat reduced and stabilized by post-growthannealing (FIG. 7(b)).

Example 10

With reference to FIG. 1, the reagents 5-bromo-2,2′-dithiophene (4), and5,5′-bis(tri-n-butylstannyl)-2,2′-dithiophene were prepared according toknown synthetic procedures. Other solvents and reagents were purchasedfrom the Aldrich or Lancaster concerns and purified as required.

Example 11

5-Perfluorohexyl-2,2′-dithiophene (5). A suspension of Cu bronze (3.38g, 53.16 mmol) in dry DMSO (30 mL) was heated at 125° C. for 15 minunder nitrogen. Perfluorohexyl iodide (11.34 g, 25.43 mmol) was addeddropwise in such a way as to keep the temperature below 135° C. After 45min, a solution of 5-bromodithiophene (2.50 g, 10.17 mmol) in the samesolvent (7.0 mL) was added dropwise, and the reaction mixture wasstirred at 125° C. for 16 h. The reaction was next quenched with coldwater (100 mL) and diethyl ether was added (200 mL). After shaking, themixture was filtered through Celite and the organic phase collected. Theaqueous layer was extracted once more with ether (100 mL) and the twoorganic phases were combined, washed with water, and dried over MgSO₄.After filtration, the solvent was evaporated to yield a solid (5.18 g)which was chromatographed on silica gel (hexane) to afford pure productas a yellow solid (2.90 g, 5.99 mmol, 58.9% yield). M.p. 51-53° C.(MeOH); ¹H NMR (CDCl₃): δ 7.31-7.37 (2H, m), 7.28 (1H, d, ²J=3.6), 7.18(1H, d, ²J=3.7), 7.06 (1H, dd); ¹⁹F NMR (CDCl₃): δ −81.07 (3F), −101.64(2F), −121.83 (4F, broad), −123.11 (2F), −126.43 (F). Anal. Calcd forC₁₄H₅F₁₃S₂: C, 34.72; H, 1.04; F, 51.00. Found: C, 34.96; H, 0.99; F,49.95; HRMS (EI, 70 eV): found m/z 483.9626, calcd for C₁₄H₅F₁₃S₂ (M⁺)483.9625.

Example 12

5-Perfluorohexyl-5′-bromo-2,2′-dithiophene (6). With exclusion of light,NBS (1.02 g, 5.73 mmol) was added to a solution of5-perfluorohexyldihiophene (2.32 g, 4.79 mmol) in DMF (32 mL). Afterstirring overnight at 25° C., the reaction mixture was poured into brine(120 mL), and the solution then extracted with ether (3×100 mL). Theorganic phase was next washed with water, dried over MgSO₄, filtered,and the solvent evaporated to afford 2.60 g of crude product. Flashchromatography on silica gel (hexane) afforded the title compound as alight yellow solid (2.10 g, 3.73 mmol, 77.8% yield). Sublimation (50°C./10⁻³ Torr) afforded a purer sample. M.p. 63-65° C.; ¹H NMR (CDCl₃) δ7.34 (1H, d,), 7.12 (1H, d, ²J=3.1), 7.03 (1H, d, ²J=3.3), 7.01 (1H, d);¹⁹F NMR (CDCl₃) δ −81.07 (3F), −101.64 (2F), −121.83 (4F, broad),−123.11 (2F), −126.43 (2F).(fluorine NMR to be recorded). Anal. Calcdfor C₁₄H₄BrF₁₃S₂: C, 29.86; H, 0.72; F, 43.86. Found: C,; H,; F,; HRMS(EI, 70 eV): found m/z 563.8721, calcd for C₁₄H₄BrF₁₃S₂ (M⁺) 563.8709.

Example 13

α,ω-Diperfluorohexyl-sexithiophene, DFH-6T (1e). A mixture of5,5′-bis(tri-n-butylstannyl)-2,2′-dithiophene (1.40 g, 1.88 mmol),5-perfluorohexyl-5′-bromo-2,2-dithiophene (2.00 g, 3.55 mmol) andPd(PPh₃)₄ (0.050 g, 0.040 mmol) in dry DMF (40 mL) was deareated twicewith nitrogen. The reaction mixture was then heated at 80° C. for 7 hduring which time a precipitate formed. After cooling, the bright orangesolid was collected and washed several times with hexane, methanol, andacetone to afford the analytically pure product (1.91 g, 1.69 mmol,95.2% yield). M.p. 309° C. Additional purification can be achieved bygradient sublimation. Anal. Calcd for C₃₆H₁₂F₂₆S₆: C, 38.24; H, 1.07; F,43.69. Found: C, 38.16; H, 1.15; F, 43.42; MS (EI, 70 eV) 1127.4 (M⁺,70%).

Example 14

With reference to structure 7, below, the compounds of this examplefurther illustrate the thiophene compositions, materials and/or films ofthe type available through this invention. (X is a functional group ofthe sort described in Example 15, and a=0-12.)

N R₁ R₂ 7a 1 C₆F₁₃ C₆F₁₃ 7b 1.5 CF₃ C₂H₄X 7c 3 C₄H₉ CF₃ 7d 4 C₃F₇(CH₂)_(a)X 7e 5-6 C₂F₅ C₈F₁₇

Example 15

In general, the oligo- and/or polythiophene compounds of this inventionincluding those of and represented by the preceding example are preparedin accordance with the synthetic procedures described herein andstraight-forward modifications thereof. Substitution of5-halo-2,2′-dithiophene with a suitable fluorocarbon provides oneintermediate (a). Alternatively, the monohalodithiophene can behalogenated through known techniques for subsequent fluorocarbonsubstitution at both the 5 and 5′ positions, such a dithiophene for useas described herein, as an n-type semiconducting material.

Yet another embodiment of this example contemplates substitution at the5′ position, and fluoroalkylation at the 5 position to provide a secondintermediate (b). The 5′ substituent introduces an aromatic or alkylmoiety including but not limited to amino, hydroxyl and/or carboxylicfunctional groups for later possible synthetic transformation.Intermediates (a) and/or (b) of this example are coupled with a stannyl(mono- or -bis-) thiophene (mono- or -di-), or further reacted withanother intermediate of the type described herein to provide a range ofconjugated thiophene units, with the desired degree of fluoroalkylationand/or alternate functionalization.

Example 16

FIG. 8 illustrates incorporation of a thiophene semiconductor materialof the present invention in an n-channel junction field-effecttransistor (JFET). The JFET includes a gate region 10 constructed from ap-type semiconductor material and a channel 12 constructed from ann-type thiophene thin film deposited on a suitable substrate. (Asmentioned above, the material of region 10 can be a p-type thiophenesemiconductor.) In this device, a voltage applied to a gate electrode 14controls current flow through the thin film/substrate composite ofchannel 12 between the drain electrode 16 and the source electrode 18.One of ordinary skill in the art can similarly apply a thiophenematerial of the present invention in a number of other transistorapplications to provide without limitation p-channel JFETs, bipolarjunction transistors of both the npn and pnp type, depletion andenhancement mode MOSFETS of both n and p channel types, and other typesof transistors and integrated circuits.

Example 17

The reagents 5-bromo-2,2′:5′,2″-terthiophene, 5-bromo-2,2′-dithiophene,and 5,5′-bis(tri-n-butylstannyl)-2,2′-dithiophene were preparedaccording to known procedures. Solvents and chemicals were purchasedfrom Aldrich or Lancaster and purified as required.

Example 17a

5-Perfluorohexyl-2,2′:5′,2″-terthiophene and5,5′-diperfluorohexyl-2,2°:5′,2″-terthiophene. A suspension of copperbronze (1.01 g, 15.9 mmol) in dry DMSO (10 mL) was heated at 125° C. for15 min under nitrogen. Perfluorohexyl iodide (3.40 g, 7.62 mmol) wasthen added dropwise in such a way as to keep the temperature below 135°C. After 45 min, a warm solution of 5-bromoterthiophene (1.00 g, 3.05mmol) in the same solvent (10 mL) was added in a single portion, and thereaction mixture was stirred at 125° C. for 14 h. Distilled cold water(60 mL) was next added to the reaction flask and the resultingprecipitate was collected on a Buchner funnel, washed several times withwater, and finally dried overnight under vacuum. The crude product (1.40g) was obtained from this solid by extraction with chloroform (3×50 mL).Column chromatography on silica gel (hexane) afforded the purefluorinated product (0.76 g, 1.34 mmol, 43.9% yield) as a light yellowsolid M.p. 158° C. (iPrOH); ¹H NMR (CDCl₃) δ 7.36 (1H, d, ²J=3.8), 7.28(1H, d, ²J=3.6), 7.22 (1H, d, ²J=3.7), 7.15-7.19 (2H, m), 7.12 (1H, d,²J=3.8), 7.06 (1H, dd); ¹⁹F NMR (CDCl₃) δ −81.10 (3F), −101.63 (2F),−121.89 (4F, broad), −123.10 (2F), −126.44 (2F). Anal. Calcd forC₁₈H₇F₁₃S₃: C, 38.17; H, 1.25; F, 43.61. Found: C, 37.95; H, 1.18; F,44.01; HRMS (EI, 70 eV): found m/z 565.9501, calcd for C₁₈H₇F₁₃S₃ (M⁺)565.9502. 5,5′-diperfluorohexyl-2,2′:5′,2″-terthiophene was obtained asbyproduct (0.18 g, 0.201 mmol, 6.7% yield). M.p. 132° C. (toluene); ¹HNMR (CDCl₃) δ 7.38 (3H, d, ²J=3.4), 7.22 (2H, d), 7.21 (2H, s); ¹⁹F NMR(CDCl₃) δ −81.08 (6F), −101.61 (4F), −121.90 (8F, broad), −123.07 (4F),−126.43 (4F). Anal. Calcd for C₂₄F₂₆S₃: C, 32.59; H, 0.685; F, 55.85.Found: C, 32.50; H, 0.69; F, 55.63; HRMS (EI, 70 eV): found m/z883.9226, calcd for C₂₄H₆F₂₆S₃ (M⁺) 883.9217.

Example 17b

5-Perfluorohexyl-2,2′-dithiophene and5,5′-diperfluorohexyl-2,2′-dithiophene. A suspension of copper bronze(3.38 g, 53.16 mmol) in dry DMSO (30 mL) was heated at 125° C. for 15min under nitrogen. Perfluorohexyl iodide (11.34 g, 25.43 mmol) wasadded dropwise in such a way as to keep the temperature below 135° C.After 45 min, a solution of 5-bromodithiophene (2.50 g, 10.17 mmol) inthe same solvent (7 mL) was added dropwise, and the reaction mixture wasstirred at 125° C. for 16 h. The reaction was next quenched with coldwater (100 mL) and diethyl ether was added (200 mL). After shaking, themixture was filtered through Celite and the organic phase collected. Theaqueous layer was extracted once more with ether (100 mL) and the twoorganic phases were combined, washed with water, and dried over MgSO₄.After filtration, the solvent was evaporated to give a solid (5.18 g)which was chromatographed on silica gel (hexane) to afford two products.5,5′-diperfluorohexyl-2,2′-dithiophene (0.70 g, 0.87 mmol, 8.6% yield)as a white solid. mp=97° C. (toluene); ¹H NMR (CDCl₃) δ 7.41 (2H, d,²J=3.5), 7.27 (1H, d); ¹⁹F NMR (CDCl₃) δ −81.05 (6F), −101.90 (4F),−121.72 (4F), −121.89 (4F), −123.09 (4F), −126.41 (4F). Anal. Calcd forC₂₀H₄F₂₆S₂: C, 29.94; H, 0.50; F, 61.57. Found: C, 29.90; H, 0.57; F,61.73; HRMS (EI, 70 eV): found m/z 801.9336, calcd for C₂₀H₄F₂₆S₂ (M⁺)801.9334. The monosubstituted system was isolated as a yellow solid(2.90 g, 5.99 mmol, 58.9% yield). M.p. 51-53° C. (MeOH); ¹H NMR (CDCl₃)δ 7.31-7.37 (2H, m), 7.28 (1H, d, ²J=3.6), 7.18 (1H, d, ²J=3.7), 7.06(1H, dd); ¹⁹F NMR (CDCl₃) δ −81.07 (3F), −101.64 (2F), −121.83 (4F,broad), −123.11 (2F), −126.43 (F). Anal. Calcd for C₁₄H₅F₁₃S₂: C, 34.72;H, 1.04; F, 51.00. Found: C, 34.96; H, 0.99; F 49.95; HRMS (EI, 70 eV):found m/z 483.9626, calcd for C₁₄H₅F₁₃S₂ (M⁺) 483.9625.

Example 17c

5-Perfluorohexyl-5′-bromo-2,2′-dithiophene. With the exclusion of light,NBS (1.02 g, 5.73 mmol) was added to a solution of5-perfluorohexyldihiophene (2.32 g, 4.79 mmol) in DMF (32 mL). Afterstirring overnight at room temperature, the reaction mixture was pouredonto brine (120 mL) and the solution then extracted with ether (3×100mL). The organic phase was next washed with water, dried over MgSO₄,filtrated, and the solvent evaporated to afford 2.60 g of crude product.Flash chromatography on silica gel (hexane) afforded the title compoundas a light yellow solid (2.10 g, 3.73 mmol, 77.8% yield). Sublimation(50° C./10⁻³ Torr) afforded a purer sample. M.p. 63-65° C.; ¹H NMR(CDCl₃) δ 7.34 (1H, d,), 7.12 (1H, d, ²J=3.1), 7.03 (1H, d, ²J=3.3),7.01 (1H, d); ¹⁹F NMR (CDCl₃) δ −81.07 (3F), −101.64 (2F), −121.83 (4F,broad), −123.11 (2F), −126.43 (2F).(fluorine NMR to be recorded). Anal.Calcd for C₁₄H₄BrF₁₃S₂: C, 29.86; H, 0.72; F, 43.86. Found: C,; H,; F,;HRMS (EI, 70 eV): found m/z 563.8721, calcd for C₁₄H₄BrF₁₃S₂ (M⁺)563.8709.

Example 17d

5-(tri-n-Butylstannyl)-5′-(1-perfluorohexyl)-2,2′-dithiophene. n-BuLi(1.6 M, 1.11 mL) was added dropwise to a solution of5-bromo-5′-(1-perfluorohexyl)-2,2′-dithiophene (1.00 g, 1.77 mmol) inTHF (15 mL) at −78° C. The reaction mixture was stirred at thistemperature for 30 min, and then for 1 h at room temperature followed bythe addition of tri-n-butyltin chloride (0.59 g, 1.80 mmol). Afterstirring for 3 h at room temperature, hexane (50 mL) was added to themixture and the organic phase was washed with a solution of NH₄Cl (5%,20 mL) and water (20 mL). The clear solution was dried over MgSO₄ andconcentrated in vacuo to afford the product as a brown oil (1.32 g, 1.71mmol, 96.6% yield). ¹H NMR (CDCl₃) δ 7.36 (1H, d, ²J=3.3), 7.32 (1H, d,²J=3.7), 7.15 (1H, d), 7.09 (1H, d), 1.54-1.60 (6H, m), 1.32-1.38 (6H,m), 1.13 (6H, t, ²J=8.1), 0.90 (9H, t, ²J=7.3); ¹⁹F NMR (CDCl₃) δ −81.28(3F), −101.70 (2F), −121.79 (2F), −122.00 (2F), −123.13 (2F), −126.43(2F). HRMS (EI, 70 eV): found m/z 774.0680, calcd for C₂₆H₄₄S₂Sn (M⁺)774.0682.

Example 17e

5,5′″-Diperfluorohexyl-2,2′:5′,2″:5″,2′″:5′″,2″″:5″″,2′″″-quaterthiophene.A mixture of5-(tri-n-butylstannyl)-5′-(1-perfluorohexyl)-2,2-dithiophene (1.31 g,1.70 mmol), 5-perfluorohexyl-5′-bromo-2,2′-dithiophene (0.96 g, 1.70mmol) and tetrakis(triphenylphosphine)palladium(0) (0.05 g, 0.04 mmol)in dry DMF (10 mL) was deareated twice with nitrogen. The reactionmixture was then heated at 95° C. for 5 h during which time aprecipitate formed. After cooling, the bright yellow solid was collectedand washed several times with methanol and Et₂O to afford theanalytically pure product (1.30 g, 1.35 mmol, 79.4% yield). M.p. 213° C.Additional purification can be achieved by gradient sublimation. ¹H NMR(C₂Cl₄D₂, ˜60° C.) δ 8.28 (2H, d, ²J=3.8), 8.09-8.14 (4H, m), 7.08 (1H,d, ²J=4.0); ¹⁹F NMR (C₂Cl₄D₂, ˜60° C.) δ −79.64 (3F), −99.88 (2F),−120.10 (4F), −121.41 (2F), −124.64 (2F). Anal. Calcd for C₂₈H₈F₂₆S₄: C,34.81; H, 0.84; F, 51.14. Found: C, 34.66; H, 0.94; F, 51.06; MS (EI, 70eV) 965.9 (M⁺, 100%).

Example 17f

3-Perfluorohexyl-2,2′-dithiophene. A suspension of copper bronze (6.76g, 106.32 mmol) in dry DMSO (60 mL) was heated at 125° C. for 15 minunder nitrogen. Perfluorohexyl iodide (22.68 g, 50.86 mmol) was addeddropwise in such a way as to keep the temperature below 135° C. After 40min, a solution of 3-bromo-2,2′-dithiophene (5.00 g, 20.34 mmol) in thesame solvent (14 mL) was added dropwise, and the reaction mixture wasstirred at 125° C. for 6 h. The reaction was next quenched with coldwater (200 mL) and diethyl ether was added (300 mL). After shaking, themixture was filtered through Celite and the organic phase was collected.The aqueous layer was extracted once more with ether (300 mL) and thetwo organic phases were combined, washed with water, and dried overMgSO₄. After filtration, the solvent was evaporated to give a brown oil(˜9 g) which was chromatographed on silica gel (hexane) to afford theproduct as a yellow oil (5.20 g, 10.74 mmol, 52.8% yield). ¹H NMR(CDCl₃) δ 7.44 (1H, dd, ²J=5.2 ³J=1.3), 7.41 (1H, d, ²J=5.5), 7.20-7.24(2H, m), 7.09 (1H, dd); ¹⁹F NMR (CDCl₃) δ −81.20 (3F), −102.95 (2F),−121.18 (2F), −122.01 (2F), −123.09 (2F), −126.43 (2F). Anal. Calcd forC₁₄H₅F₁₃S₂: C, 34.72; H, 1.04; F, 51.00. Found: C, 35.01; H, 1.04; F,49.98; HRMS (EI, 70 eV): found m/z, calcd for C₁₄H₅F₁₃S₂ (M⁺).

Example 17g

3-(1-Perfluorohexyl)-5′-bromo-2,2′-dithiophene. In the absence of lightNBS (1.47 g, 8.26 mmol) was added portionwise to a solution of3-(1-perfluorohexyl)-2,2′-dithiophene (4.00 g, 8.26 mmol) in DMF (70 mL)at −30° C. over the period of 6 h. The reaction mixture was left toslowly reach room temperature and, after stirring overnight, was pouredonto water (100 mL). The aqueous phase was extracted with ether (3×100mL) and the combined ethereal phases were washed with water and driedover MgSO₄. The solvent was evaporated leaving a brown oil (4.35 g),which was chromatographed on silica gel (hexane) to afford the titlecompound as a light yellow oil (3.67 g, 6.51 mmol, 78.8% yield). ¹H NMR(CDCl₃) δ 7.42 (1H, d, ²J=5.5), 7.21 (1H, d), 6.40 (1H, d, ²J=3.9), 6.96(1H, d). ¹⁹F NMR (CDCl₃) δ −81.18 (3F), −103.35 (2F), −121.26 (2F),−122.10 (2F), −123.19 (2F), −126.51 (2F). HRMS (EI, 70 eV): found m/z,calcd for C₁₄H₄BrF₁₃S₂ (M⁺).

Example 17h

3,3′″″-Diperfluorohexyl-2,2′:5′,2″:5″,2′″:5′″,2″″:5″″,2′″″-sexithiophene.A mixture of 5,5′-bis(tri-n-butylstannyl)-2,2-dithiophene (2.00 g, 3.55mmol), 5-perfluorohexyl-5′-bromo-2,2′-dithiophene (1.40 g, 1.88 mmol)and tetrakis(triphenylphosphine)palladium(0) (0.05 g, 0.04 mmol) in dryDMF (40 mL) was deareated twice with nitrogen. The reaction mixture wasthen heated at 90° C. overnight during which time a precipitate formed.After cooling, the bright orange solid was collected and washed severaltimes with ether to afford the analytically pure product (1.80 g, 1.59mmol, 89.6% yield). M.p. 217° C. Additional purification can be achievedby gradient sublimation. ¹H NMR (C₂Cl₄D₂, 110° C.) δ 7.43 (2H, d,²J=5.6), 7.24 (1H, d), 8.14-8.19 (8H, m); ¹⁹F NMR(C₂Cl₄D₂, 110° C.) δ−81.30 (6F), −102.22 (4F), −120.71 (2F), −121.51 (4F), −122.68 (4F),−125.94 (4F). Anal. Calcd for C₃₆H₁₂F₂₆S₆: C, 38.24; H, 1.07; F, 43.69.Found: C, 38.41; H, 1.07; F, 43.60.

Example 18a

5,5′-Bis[1-(4-bromo-2,3,5,6-tetrafluorophenyl)]-2,2′-dithiophene. Amixture of 5,5′-bis(tri-n-butylstannyl)-2,2′-dithiophene (4.62 g, 4.87mmol), 1,4-dibromoperfluorobenzene (6.00 g, 19.48 mmol) andtetrakis(triphenylphosphine)palladium(0) (0.12 g, 0.10 mmol) in dry DMF(20 mL) was deareated twice with nitrogen. The reaction mixture was thenheated at 85° C. for 20 h during which time a precipitate formed. Aftercooling, the orange solid was collected and washed several times withhexane and ether to afford the crude product which was purified bygradient sublimation (2.14 g, 3.42 mmol, 70.2% yield). M.p. 231° C. ¹HNMR (CDCl₃) δ 7.60 (2H, d, ²J=4.1), 7.34 (2H, d); ¹⁹F NMR (CDCl₃) δ−133.58 (4F), −138.5.6 (4F). Anal. Calcd for C₂₀H₄Br₂F₈S₂: C, 38.72; H,0.65; F, 24.51. Found: C, 38.75; H, 0.78; F, 24.29.

Example 18b

5,5′-Bis{1-[4-(thien-2-yl)-2,3,5,6-tetrafluorophenyl)]}-2,2′-dithiophene.A mixture of 2-(tri-n-butylstannyl)thiophene (1.35 g, 3.63 mmol),5,5′-bis[1-(4-bromo-2,3,5,6-tetrafluorophenyl)]-2,2′-dithiophene (0.75g, 1.20 mmol) and tetrakis(triphenylphosphine)palladium(0) (0.02 g, 0.02mmol) in dry toluene (20 mL) was deareated twice with nitrogen. Thereaction mixture was refluxed for 20 h during which time a precipitateformed. After cooling, the orange-gold solid was collected and washedseveral times with hexane and ether to afford the pure product aftergradient sublimation (0.55 g, 0.88, 73.3% yield). M.p. 319° C. ¹H NMR(C₂Cl₄D₂, 125° C.) δ 7.71 (1H, d, ²J=3.8), 7.66 (1H, d, ²J=3.9), 7.62(1H, d, ²J=4.6), 7.40 (1H, d), 7.26 (1H, dd); ¹⁹F NMR (C₂Cl₄D₂, 125° C.)δ −140.91 (8F). Anal. Calcd for C₂₈H₁₀F₈S₄: C, 53.67; H, 1.61; F, 24.26.Found: C, 53.80; H, 1.71; F, 24.35.

Example 18c

2-Perfluorophenylthiophene. A mixture of 2-(tri-n-butylstannyl)thiophene(15.0 g, 40.50 mmol), bromoperfluorobenzene (10.00 g, 40.50 mmol),tetrakis(triphenylphosphine)palladium(0) (0.92 g, 0.80 mmol) and fewcrystals of 2,6-di-tert-butyl-4-methylphenolo in dry toluene (80 mL) wasdeaerated twice with nitrogen. The reaction mixture was refluxed 24 hand, after cooling, poured onto a solution of NH₄F (5 g, 200 mL ofwater). After stirring for 30 min, hexane (300 mL) and acetone (150 mL)were added and the mixture was filtered over celite. The organic phasewas separated, dried over MgSO₄, and the solvent was evaporated toafford a brown oil (18.36 g), which was chromatographed on silica gel(hexane) to give the pure product as a white solid (8.25 g, 32.97 mmol,81.41% yield). M.p.=44° C. ¹H NMR (CDCl₃) δ (1H, dd, ²J=5.2, ³J=0.9),(1H, dd, ²J=3.5), (2H, m). ¹⁹F NMR (CDCl₃) δ −(4F), −(4F). HRMS (EI, 70eV): found m/z, calcd for C₁₀H₃F₅S (M⁺).

Example 18d

2-Perfluorophenyl-5-bromothiophene. In the absence of light NBS (2.45 g,13.79 mmol) was added to a solution of 2-perfluorophenylthiophene (300g, 11.99 mmol in DMF (50 mL). After stirring overnight at roomtemperature, iced water (200 mL) was added and the precipitate wascollected, washed with water, and dried under vacuum to afford the pureproduct as a white solid (3.70 g, 11.24 mmol, 93.7% yield). Mp=79° C. ¹HNMR (CDCl₃) δ 7.30 (1H, d, ²J=4.0), 7.16 (1H, d). ¹⁹F NMR (CDCl₃) δ−140.04 (1F), −155.07 (2F), −161.65 (2F). HRMS (EI, 70 eV): found m/z,calcd for C₁₀H₂BrF₅S (M⁺).

Example 18e

5,5′″-Diperfluorophenyl-2,2′:5′,2″:5″,2′″:5′″,2″″:5″″,2′″″-quaterthiophene.A mixture of 5,5′-bis(tri-n-butylstannyl)-2,2′-dithiophene (2.26 g, 3.04mmol), 2-perfluorophenyl-5-bromothiophene (2.00 g, 6.08 mmol) andtetrakis(triphenylphosphine)palladium(0) (0.07 g, 0.06 mmol) in dry DMF(40 mL) was deareated twice with nitrogen. The reaction mixture wasrefluxed overnight during which time a precipitate formed. Aftercooling, the orange solid was collected and washed several times withhexane, MeOH, and ether to afford the pure product as an orange solid(1.58 g, 2.38 mmol, 78.3% yield). Additional purification can beachieved by gradient sublimation. M.p. 246° C. ¹H NMR (C₂Cl₄D₂, 125° C.)δ 7.50 (2H, d, ²J=3.5), 7.29 (2H, d), 7.23 (2H, d, ²J=3.8), 7.19 (1H,d); ¹⁹F NMR (C₂Cl₄D₂, 125° C.) δ −140.03 (2F), −156.40 (4F), −162.66(4F). Anal: Calcd for C₂₈H₈F₁₀S₄: C, 50.75; H, 1.22; F, 28.67. Found: C,50.85, H, 1.28; F, 28.95.

Example 19a

4,6-Di(thien-2-yl)pyrimidine. A mixture of tri-n-butylstannylthiophene(10.52 g, 28.19 mmol), 4,6-dichloropyrimidine (2.00 g, 13.42 mmol),tetrakis(triphenylphosphine)palladium(0) (0.345 g, 0.30 mmol) and fewcrystals of 2,6-di-tert-butyl-4-methylphenolo in dry toluene (20 mL) wasdeareated twice with nitrogen. The reaction mixture was refluxed for 6hours and, after cooling, a white precipitate was formed in the reactionflask. The solid was collected and the organic phase was diluted withether (100 mL), poured onto a solution of NH₄F (3 g, 100 ml) andseparated. After drying over MgSO4, the solvent was evaporated affordinga solid material. The two solid phase were combined and crystallizedfrom toluene to give the pure product as a white crystals (2.36 g, 9.66mmol, 72.0% yield). mp 146° C.; ¹H NMR (CDCl₃) δ 9.07 (1H, d, ²J=1.4),7.86 (1H, d, ²J=3.7), 7.83 (1H, d), 7.57 (1H, d, ²J=5.1), 7.20 (1H, dd).

Example 19b

5,5′-Bis-(6-chloropyrimid-4-yl)-2,2′-dithiophene. A mixture of5,5′-bis(tri-n-butylstannyl)-2,2′-dithiophene (7.58 g, 10.18 mmol),4,6-dichloropyrimidine (6.00 g, 40.27 mmol) andtetrakis(triphenylphosphine)palladium(0) (0.26 g, 0.22 mmol) in drytoluene (70 mL) was deareated twice with nitrogen. The reaction mixturewas refluxed for 6 hours and, after cooling, the precipitate wascollected. The solid residue was washed several times with hexane andthan with methanol to afford the practically pure compound as a yellowpowder (2.80 g, 7.16 mmol, 70.3% yield). mp 261° C. (sublimation); ¹HNMR (CDCl₃) δ 8.91 (2H, d, ²J=1.3), 7.73 (2H, d, ²J=4.0), 7.60 (2H, d),7.37 (2H, d,). ms 390.9(100%) 392.9 (75%). Anal. Calcd for C₁₆H₈Cl₂N₄S₂:C, 49.11; H, 2.06; N, 14.32. Found: C, 49.21; H, 2.19; N, 14.16.

Example 19c

5,5′-Bis[6-(thien-2-yl)pyrimidyl-4-yl)-2,2′-dithiophene. A mixture of5,5′-bis(6-chloropyrimid-4-yl)-2,2-dithiophene (1.40 g, 3.58 mmol),tri-n-butylstannylthiophene (3.00 g, 8.04 mmol),tetrakis(triphenylphosphine)palladium(0) (0.20 g, 0.17 mmol) and fewcrystals of 2,6-di-tert-butyl-4-methylphenolo in dry toluene (120 mL)was deareated twice with nitrogen. The reaction mixture was refluxed for10 hours and, after cooling, the precipitate was collected (2.00 g). Thesolid residue was washed several times with hexane and than crystallizedfrom pyridine (170 mL) to afford the pure compound as an orange solid(0.88 g, 1.81 mmol, 50.5% yield). Extremely pure samples can be obtainedafter gradient sublimation. mp=306° C.; ¹H NMR (CDCl₃) δ 9.09 (2H, d,²J=1.2), 7.94 (2H, d, ²J=3.7), 7.85 (2H, d, ²J=4.0), 7.83 (2H, d), 7.61(2H, d, ²J=4.9), 7.41 (2H, d), 7.24 (2H, dd). ms 487.0 (100%). Anal.Calcd for C₂₄H₁₄N₄S₄: C, 59.23; H, 2.91; N, 11.52. Found: C, 59.17; H,2.97; N, 11.37.

Example 19d

5,5′-Bis[6-(5-hexylthien-2-yl)pyrimid-4-yl)-2,2′-dithiophene. A mixtureof 5,5′-bis(6-chloropyrimid-4-yl)-2,2′-dithiophene (1.05 g, 2.68 mmol)),2-(tri-n-butylstannyl)-5-hexylthiophene (2.60 g, 5.68 mmol),tetrakis(triphenylphosphine)palladium(0) (0.15 g, 0.13 mmol) and fewcrystals of 2,6-di-tert-butyl-4-methylphenolo in dry toluene (90 mL) wasdeareated twice with nitrogen. The reaction mixture was refluxed for 12hours and, after cooling, the precipitate was collected bycentrifugation (1.66 g). The solid residue was washed once with hexaneand than dissolved in hot chloroform (150 mL). The warm solution wasfiltered and the solvent evaporated to give the pure product as a brownsolid (1.21 g, 1.85 mmol, 71.1% yield). An analytical sample wascrystallized from toluene and sent to the elemental analysis. mp=230°C.; ¹H NMR (CDCl₃) δ ???? (2H, d, ²J=1.2), ???? (2H, d, ²J=3.7), (2H, d,²J=4.0), (2H, d), (2H, d, ²J=4.9), (2H, d), (2H, dd). Anal. Calcd forC₃₆H₃₈N₄S₄: C, 66.01; H, 5.86; N, 8.56. Found: C, 65.88; H, 5.57; N,8.57.

Example 19e

3-(Thien-2-yl)-6-chloropyridazine. A mixture oftri-n-butylstannylthiophene (6.26 g, 16.78 mmol), 3,6-dichloropyridazine(5.00 g, 33.56 mmol), tetrakis(triphenylphosphine)palladium(0) (0.20 g,0.17 mmol) and few crystals of 1,2-ditert-butyl of2,6-di-tert-butyl-4-methylphenolo in dry DMF (50 mL) was deareated twicewith nitrogen. The reaction mixture was heated at 80° C. for 6 hoursand, after cooling, poured onto water (100 mL). A white precipitate wascollected, washed several times with water and dried under vacuum. Thissolid was taken up with ether (25 mL) and filtered to afford 3.01 g ofalmost pure product. Finally, this solid was crystallized from MeOH—H₂Oto give the pure target compound as white crystals (1.56 g, 7.90 mmol,47.3% yield). Mp 155° C.; ¹H NMR (CDCl₃) δ 7.75 (1H, d, ²J=11.0), 7.68(1H, d, ²J=3.6), 7.54 (1H, d, ²J=5.0), 7.51 (1H, d), 7.18 (1H, dd).

Example 19f

5,5′-Bis[6-(thien-2-yl)pyridazin-3-yl)]-2,2′-dithiophene. A mixture of3-(thien-2-yl)-6-chloropyridazine (1.50 g, 7.63 mmol),5,5′-bis(tri-n-butylstannyl)-2,2′-dithiophene (2.84 g, 3.81 mmol), andtetrakis(triphenylphosphine)palladium(0) (0.09 g, 0.08 mmol) in dry DMF(30 mL) was deareated twice with nitrogen. The reaction mixture washeated at 70° C. overnight. After cooling, the precipitate wascollected, washed several times with hexane, MeOH, and ether. Afterdrying the pure product was obtained as a light orange solid (1.60 g,3.29, 86.3% yield). mp>350° C. Anal. Calcd for C₂₄H₁₄N₄S₄: C, 59.23; H,2.91; N, 11.52. Found: C, 58.85; H, 3.11; N, 11.57.C.

Example 20

The data of the following examples illustrate the impact of bothperfluoroalkyl and perfluorophenyl/azine substitution on the chemical,thermal, optical and electronic properties of the π-conjugated core bythermal (DSC, TGA), molecular spectroscopy (UV-Vis, PL), andelectrochemical (CV, DPP), techniques. Reference systems are theunsubstituted (6T) and α,ω-dihexyl substituted (DH-6T) sexithiophenes ofthe prior art. Morphological and crystal structure data are alsoprovided.

Example 20a

With reference to FIG. 2 (and Example 2), the α,ω-fluorocarbon chainshave a dramatic effect on the volatility of most of systems 1-3 (FIG.9). The monotonic % weight retention vs. T demonstrates smooth, clean,quantitative sublimation well below the melting point with negligibleresidue. In contrast, DH-6T (FIG. 2) exhibits significant volatilityonly above the melting point, with the TGA data revealing inflections at≈298 and ≈306° C., suggesting decomposition processes. In addition, asignificant decomposition-related residue (≈6%) is observed at 320° C.

Example 20b

Absorption and fluorescence emission spectra were recorded to monitorthe effect of substitution on the HOMO-LUMO energy gap. By varying thenumber of thiophene units, it is possible to modulate optical absorptionfrom 300 to 500 nm (FIG. 10). On the other hand, fluorophenyl-azineinsertion into the 6T core allows for a very fine tune in the range of450-500 nm (Table 1). Film PL intensities change of many orders ofmagnitude with chemical structure. DFH-6T and iso-DFH-6T were found muchmore efficient that the corresponding unsubstituted and dialkylsubstituted systems. 2a is substantially more efficient than 2b in spiteof the similar solution absorption/emission and film absorptionpatterns. Comparative spectra are also shown in FIGS. 11-12. TABLE 1Absorption (γ_(max), nm) Data in Toluene Solution and as Thin Film (ca.1.8 μm). γ_(max) Compound Solution Film DFH-2T 348 DFH-3T 411 DFH-4T 456429 isoDFH-6T 482 461 DFH-6T 492 526 DH-6T 497 535 BFT4BF 475 456TBFT2BFT 452 419 BrBFT2BFBr 428 TPMT2PMT 451 TPDT2PDT 462

TABLE 2 HOMO-LUMO Energy Gap (E_(g), eV) from Optical Data. E_(g)Compound Solution Film DFH-2T 3.57 DFH-3T 3.02 DFH-4T 2.72 2.89isoDFH-6T 2.58 2.69 DFH-6T 2.52 2.36 DH-6T 2.50 2.32 BFT4BF 2.61 2.72TBFT2BFT 2.75 2.96 BrBFT2BFBr 2.9 TPMT2PMT 2.75 TPDT2PDT 2.69

Example 20c

The effects of fluoroalkyl, fluorophenyl, and azinesubstitution-insertion were also investigated by cyclic voltammetry(one-compartment cell with Pt electrode, bare Ag reference, Pt counterelectrodes). Results are collected on Table 3. Voltammograms of most ofthe investigated systems in THF/0.10M TBABF₄ exhibit two chemicallyoxidative and reductive peeks (FIGS. 13 and 14). Note that the first andsecond anodic peaks of DFH-6T vs. DH-6T exhibit a uniform anodic shift(≈+0.27 V), indicating that introduction of perfluoroalkyl chains on the6T core substantially increases the ionization potential. The similarHOMO-LUMO gaps of DFH-6T and DH-6T argue that the LUMO of DFH-6T is alsoca. 0.27 V below that of DH-6T, which is confirmed by electrochemicalstudies on thin films. TABLE 3 Anodic (E_(a)), Cathodic(E_(c)), andStandard (E°) Potentials of Compounds 1a-c, 1h, 2a-b, 3a, and, 3c inTHF. Oxidation Potentials Reduction Potentials Compound standard anodiccathodic standard anodic cathodic anodic cathodic E_(a1) E_(a2) E_(c1)E_(c2) E°₁ E°₂ E_(a1) E_(a2) E_(c1) E_(c2) E°₁ E°₂ DFH-2T 1.49 −1.45DFH-3T 1.39 −1.48 DFH-4T 1.31 −0.95 −1.75 −0.76 −1.40 −0.85 −1.57isoDFH-6T 1.01 1.23 0.88 1.06 0.94 1.14 −1.47 1.97 1.06 −1.74 −1.26−1.86 BFT4BF 1.07 1.56 0.89 1.44 0.98 1.50 −1.56 −2.14 −1.38 −1.96 −1.47TBFT2BFT 1.43 −1.80 −1.94 −1.70 −1.83 −1.75 −1.88 TPMT2PMT 1.42 1.691.16 1.41 1.29 1.55 −1.74 −1.87 −1.60 −1.75 −1.67 TPDT2PDT 1.14 1.44−1.57 −2.01 −1.35 −1.80 −1.79 −1.90

Example 20d

A morphological study on evaporated DFH-6T thin films was providedabove, Example 6 and FIG. 6. In comparison thereto, general amorphous1c, 1h, 2a, 2b, 3a, 3c films can be prepared by rapid evaporation oncold substrates (glass, quartz, silicon). Lower evaporation rates and/orhigher substrate temperatures produce much higher orderedmicrostructures and larger crystalline domains (from SEM data). Inaddition, thanks to the great volatility of these systems annealing ofamorphous films for short period of times dramatically improvesmicrostructure order.

Example 20e

Molecular packing diagrams of DFH-3T and 2a are shown in FIGS. 16 and17, respectively. The crystal structure clearly shows the close π-πstacking intermolecular arrangement in these systems, and as can beobserved and/or utilized in various other embodiments of this invention.

The preceding examples and data confirm that the n-typethiophene-modified systems of this invention are more chemically andthermally stable than the corresponding p-type π-isoelectronic oligo-and polythiophenes and can be transported quantitatively into the gasphase without decomposition. In particular, fluoro-azinesubstitution-insertion allows for an effective modulation of opticalabsorption-emission maximum, optical gap, and photoluminescentefficiencies (quantum yields) both in solution and as thin-depositedfilms. By combining the electrochemical and optical data, absoluteorbital energies can be estimated. HOMO(LUMO) energies can be determinedfrom the first oxidation(reduction) potentials. Modification of anall-thiophene framework by introduction of powerful electron-withdrawinggroups or electron-poor heterocycles decreases MO energy levels,allowing for an easier electron injection. Depending on chemical natureof the system, deposition method (evaporation, spin-coating, casing),substrate temperature and pretreatment, either highly ordered oramorphous solids can be produced.

While the principles of this invention have been described in connectionwith specific embodiments, it should be understood clearly that thesummary and descriptions herein, along with the chosen tables, graphsand data provided, are made only by way of example and are not intendedto limit the scope of this invention in any manner. For example, avariety of the thiophene materials, of the type described herein, can beutilized as thin films incorporated into a wide range of electronicdevices. Such devices and any related circuitry can be fabricated usingcomplementary (n-type and p-type) thiophene materials. The chemical andcorresponding physical properties of such compositions/materials such asn-type conductivity, electron affinity and electron mobility can bemodified, as described herein, by choice of thiophene structure,fluoroalkyl substitution and/or heterocycle insertion, suchmodifications as may be desired for a particular end use application.Likewise, the substitution and/or insertion methods disclosed herein canalso be applied to various non-thiophene systems, to alter electronicproperties and/or provide n-type conductivity. Other advantages andfeatures of this invention will become apparent from the foregoing andany claims made thereto, with the scope thereof determined by thereasonable equivalents, as would be understood by those skilled in theart.

1-10. (canceled)
 11. An n-type polythiophene composition having thestructural formula

wherein R₁, R₂ and R₃ are substituents selected from fluoroalkylmoieties, C_(n)H_(2n+1) and where n ranges from 1-about 12, H, F, and(CH₂)_(a)X and where a ranges from 1-about 12 and X is selected fromamino, hydroxy and carboxylic acid functionalities; and x, is an integerselected from the group of integers consisting of 1 and integers greaterthan 1; y is an integer selected from the group of integers consistingof 0 and integers greater than 0, providing said composition comprisesat least one said non-thiophenyl component; z is an integer selectedfrom the group of integers consisting of 0 and integers greater than 0;and A, B, W and Z are moieties selected from N and CH.
 12. The n-typepolythiophene composition of claim 11 wherein said fluoroalkyl moiety isselected from the group consisting of linear fluoroalkyl substituents,branched fluoroalkyl substituents and cyclic fluoroalkyl substituents.13. The n-type polythiophene composition of claim 12 wherein saidfluoroalkyl moiety has the structural formula C_(n)F_(2n+1), where n is1-about
 8. 14. The n-type polythiophene composition of claim 11 whereinx is 1-about 4; y is 1-about 8; and z is 1-about
 12. 15. The n-typepolythiophene composition of claim 14 wherein said fluoroalkyl moietyhas the structural formula C_(n)F_(2n+1), where n is 1-about
 8. 16-22.(canceled)